A monocrystal of a base material such as silicon has been necessary for manufacturing a semiconductor material. As a method of manufacturing a monocrystal, Czochralski method (CZ method) has been typically known (for instance, see Patent Documents 1 and 2). Also, a method of controlling resistivity of a monocrystal has been known in which a volatile dopant such as arsenic, red phosphorus, or antimony is added to a known silicon melt used in the Czochralski method (for instance, see Patent Document 3).
In a device disclosed in Patent Document 1, a gas flow straightening inner cylindrical member is disposed above a silicon melt accommodated in a crucible. A heat insulating ring is integrated with a lower end of the gas flow straightening inner cylindrical member so as to project radially and outwardly. In addition, a gas flow straightening outer cylindrical member is integrated with an outer circumferential edge of the heat insulating ring so as to have an outer circumference facing to an inner circumference of the quartz crucible and extend upwardly.
For growing a monocrystal, inert gas is introduced to flow downwardly in the gas flow straightening inner cylindrical member to be blown onto a surface of a material melt. The inert gas subsequently flows along the surface of the material melt and further flows through a lower edge of the gas flow straightening inner cylindrical member and a lower surface of the heat insulating ring to turn upwardly. Then, the inert gas flows upwardly along an inner wall surface of the quartz crucible to be discharged to the outside of the crucible.
In a device disclosed in Patent Document 2, a gas flow straightening cylinder is disposed above a silicon melt accommodated in a crucible. A heat insulating ring is attached to a lower end of the gas straightening cylinder.
For growing a monocrystal, inert gas is introduced to flow downwardly in the gas flow straightening cylinder to be blown onto a surface of a material melt. Further, the inert gas flows along the surface of the material melt and further flows through a lower edge of the gas flow straightening cylinder to turn upwardly. Then, the inert gas flows through a space between the heat insulating ring and an inner wall of the crucible to be discharged into a furnace body. More specifically, the flow velocity of the inert gas flowing through the space between the heat insulating ring and the inner wall of the crucible is adjusted to be 6.5 cm/sec.
In a device disclosed in Patent Document 3, four purge-gas nozzles are disposed at 90 degrees intervals around the central axis of a crucible.
For growing a monocrystal silicon rod, high velocity gas is delivered through the purge-gas nozzles to maintain a predetermined ambiance on a silicon melt containing additives such as arsenic. In other words, gas curtains substantially shaped in a cylinder are provided around the central axis of the crucible. Specifically, a first gas curtain is provided to flow downwardly outside a periphery of an open top of the crucible at a velocity which creates a region of low pressure within a crystal growth chamber radially outwardly from the open top of the crucible, and a second gas curtain is provided radially inwardly of the periphery of the open top of the crucible at a radially inner side of the first gas curtain.
Patent Document 1: JP-A-2002-321997
Patent Document 2: JP-A-2002-97098
Patent Document: JP-A-10-182289